The present invention relates to a flame-retardant electrical insulating oil composition.
In the past, as a flame-retardant electrical insulating oil, a polybiphenyl chloride was employed, but after its use was forbidden from the viewpoint of environmental pollution, a silicone oil, an SF.sub.6 gas or the like has instead been utilized in, for example, vehicular or indoor transformers in which dangers of fires should be avoided. Further, it has also been suggested to employ, in a transformer or a capacitor, an insulating oil with which a phosphoric ester is mixed. However, these materials are expensive and their uses are limited due to their quality. Therefore it is now desired to develop a nonflammable or a flame-retardant insulating oil which is better in performance.
As a result of intensive research, the inventors of the present case have succeeded in developing an insulating oil excellent in flame-retardant properties and without impairing any quality inherent in the insulating oil, by adding a small amount of a halogen-containing phosphoric ester to the insulating oil.